USGS

DEPTH-DURATION FREQUENCY OF PRECIPITATION FOR OKLAHOMA

 

By Robert L. Tortorelli, Alan Rea, and William H. Asquith

 

Prepared in Cooperation with the Oklahoma Department of Transportation

 

This report is also available as a pdf.

 

U.S. Geological Survey Water-Resources Investigations Report 994232


 

ABSTRACT

A regional frequency analysis was conducted to estimate the depth-duration frequency of precipitation for 12 durations in Oklahoma (15, 30, and 60 minutes; 1, 2, 3, 6, 12, and 24 hours; and 1, 3, and 7 days). Seven selected frequencies, expressed as recurrence intervals, were investigated (2, 5, 10, 25, 50, 100, and 500 years). L-moment statistics were used to summarize depth-duration data and to determine the appropriate statistical distributions. Three different rain-gage networks provided the data (15minute, 1-hour, and 1-day). The 60-minute, and 1-hour; and the 24-hour, and 1-day durations were analyzed separately.

Data were used from rain-gage stations with at least 10-years of record and within Oklahoma or about 50 kilometers into bordering states. Precipitation annual maxima (depths) were determined from the data for 110 15-minute, 141 hourly, and 413 daily stations.

The L-moment statistics for depths for all durations were calculated for each station using unbiased L-mo-ment estimators for the mean, L-scale, L-coefficient of variation, L-skew, and L-kur-tosis. The relation between L-skew and L-kurtosis (L-moment ratio diagram) and goodness-of-fit measures were used to select the frequency distributions. The three-parameter generalized logistic distribution was selected to model the frequencies of 15-, 30-, and 60-minute annual maxima; and the three-parameter generalized extreme-value distribution was selected to model the frequencies of 1-hour to 7-day annual maxima.

The mean for each station and duration was corrected for the bias associated with fixed interval recording of precipitation amounts. The L-scale and spatially averaged L-skew statistics were used to compute the location, scale, and shape parameters of the selected distribution for each station and duration. The three parameters were used to calculate the depth-duration-frequency relations for each station. The precipitation depths for selected frequencies were contoured from weighted depth surfaces to produce maps from which the precipitation depth-duration-frequency curve for selected storm durations can be determined for any site in Oklahoma.

CONTENTS

Abstract

Introduction

Purpose and scope

Previous studies

Climate of Oklahoma

Acknowledgments

Data base of precipitation annual maxima

Data sources

Correction of precipitation annual maxima for fixed-interval recording

Regionalization of precipitation annual maxima

L-moments

L-moment ratio diagrams and goodness-of-fit measures

Spatial averaging of L-coefficient of variation and L-skew and estimation of L-scale

Contouring of depth-duration frequency

Depth-duration frequency of precipitation for Oklahoma

Error analysis

Precipitation intensity-duration frequency curve

Comparison to previous studies

Oklahoma Mesonet

Summary

Selected references


 

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